Free Astronomy Magazine September-October 2020

44 SEPTEMBER-OCTOBER 2020 SPACE CHRONICLES the star. “It would be highly unusual for such a massive star to disappear without producing a bright supernova explo- sion,” says Allan. The group first turned the ESPRESSO instrument to- ward the star in August 2019, using the VLT’s four 8-metre telescopes simul- taneously. But they were unable to find the signs that previously pointed to the presence of the luminous star. A few months later, the group tried the X-shooter in- strument, also on ESO’s VLT, and again found no traces of the star. “We may have detected one of the most massive stars of the local Uni- verse going gently into the night,” says team- member Jose Groh, also of Trinity College Dublin. “Our discovery would not have been made without using the powerful ESO 8-metre telescopes, their unique instrumentation, and the prompt ac- cess to those capabilities following the recent agreement of Ireland to join ESO.” Ireland be- came an ESO member state in September 2018. The team then turned to older data collected using X- shooter and the UVES instrument on ESO’s VLT, located in the Chilean Atacama desert, and telescopes elsewhere. “The ESO Science Archive Facil- ity enabled us to find and use data of the same object obtained in 2002 and 2009,” says Andrea Mehner, a staff astronomer at ESO in Chile who par- ticipated in the study. “The comparison of the 2002 high-resolution UVES spectra with our observations obtained in 2019 with ESO's newest high-resolution spectro- graph ESPRESSO was es- pecially revealing, from both an astronomical and an instrumentation point of view.” The old data indicated that the star in the Kin- man Dwarf could have been undergoing a strong outburst period that likely ended some- time after 2011. Lumi- nous blue variable stars such as this one are prone to experiencing giant outbursts over the course of their life, caus- ing the stars’ rate of mass loss to spike and their luminosity to in- crease dramatically. Based on their observa- tions and models, the astronomers have suggested two explanations for the star’s disappearance and lack of a supernova, related to this possi- ble outburst. The outburst may have resulted in the luminous blue vari- able being transformed into a less luminous star, which could also be partly hidden by dust. Alternatively, the team says the star may have col- lapsed into a black hole, without producing a supernova explosion. This would be a rare event: our cur- rent understanding of how massive stars die points to most of them end- ing their lives in a supernova. Future studies are needed to confirm what fate befell this star. Planned to begin operations in 2025, ESO’s Ex- tremely Large Telescope (ELT) will be capable of resolving stars in distant galaxies such as the Kinman Dwarf, helping to solve cosmic mysteries such as this one. ! I mage of the Kinman Dwarf galaxy, also known as PHL 293B, taken with the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 in 2011, before the disappearance of the massive star. Located some 75 million light-years away, the galaxy is too far away for astronomers to clearly resolve its individual stars, but in observations done between 2001 and 2011, they detected the signatures of the massive star. These signatures were not present in more recent data. [NASA, ESA/Hubble, J. Andrews (U. Arizona)] T his video starts by showing a wide-field view of a region of the sky in the constellation of Aquarius. It then zooms in to show the Kinman Dwarf galaxy, where a mysterious luminous blue variable star disap- peared. The end of the video shows an artistic anima- tion of what the star could have looked like before it disappeared. [ESO/L. Calçada, Digitized Sky Survey 2, N. Risinger (skysurvey.org ), NASA, ESA/Hubble, J. An- drews (U. Arizona) Music: Konstantino Polizois]